JPH07264151A - Pilot signal detection circuit and pilot signal detection method - Google Patents

Abstract

PURPOSE:To reduce the detection required time by locating a preprocessing multiplier circuit and a low pass filter circuit to a pre-stage at an input side and eliminating effectively a noise. CONSTITUTION:A pilot signal is respectively multiplied with a reference signal at each of multipliers 2, 3 and LPFs 4, 5 generates signals Q1, Q2 from which a harmonic component is eliminated. The signal Q1 is fed to multipliers 6, 8 and the signal Q2 is fed to multipliers 7,9 and the reference signal is fed to each multiplier. Output signals P1, P2 of the multipliers 6, 7 are fed to an adder 10 and output signals P3, P4 of the multipliers 8, 9 are fed to an adder 11 respectively and sum signals U1, U2 are respectively generated. LPFs 12, 13 receive the signals U1, U2 and eliminate the harmonic components to generate signals V1, V2, and the signals V1, V2 are fed to an amplitude evaluation circuit 14. The circuit 14 evaluates the amplitude of the signals V1, V2 to discriminate a multiplex voice mode in a broadcast signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pilot signal detecting device and a pilot signal detecting method, and more particularly to a pilot signal detecting circuit and a pilot signal detecting method used in a two-carrier audio multiplex system which is one of the multiplex systems of television signals. Regarding

[0002]

2. Description of the Related Art Television sound multiplex broadcasting is a system in which a plurality of audio channels of television broadcasting are provided and a dual audio program such as a bilingual program or a stereo audio program is broadcast. One of them is the International Commission on Wireless Communications (CCIR Document), Report 795.
The two-carrier audio multiplex system described in No. 1, 1978-1982, pp. 205-213 is used in European television systems such as the PAL system.

The outline of the present system will be described with reference to FIG. 2 showing a frequency spectrum diagram of the two-carrier audio multiplex system. The audio signal is composed of an original audio carrier of the target television system and an additional audio carrier higher than that. FM of one carrier
Sent by modulation. This is received, and the first and second audio IF (intermediate frequency) signals corresponding to these two carrier waves are obtained. These first and second audio IF signals are F
M detection is performed and the corresponding first and second audio signals are output. These first and second audio signals respectively correspond to whether the type of audio multiplexed signal is stereo or dual audio, and the first audio signal is the L + R signal or the main audio signal, and the second audio signal is the audio signal. The 2R signal or the sub audio signal is included, respectively. The pilot signal for identifying the voice multiplex signal is also included in the second voice signal. This pilot signal uses a signal having a frequency of 3.5 times the horizontal synchronizing signal of the video signal (hereinafter referred to as 3.5f _H ) as a carrier wave, and f _H / 133 in the case of a stereo identification signal compatible with stereo broadcasting.
At a frequency of (about 117.5 Hz), f _H / 57 (about 274.1) in the case of a dual audio identification signal compatible with dual audio broadcasting.
It is a signal that is AM-modulated with a modulation factor of 50% at a frequency of (Hz). The detection of the pilot signal is mainly intended to determine the current multiple voice broadcasting mode by detecting the frequencies of the AM-modulated stereo and dual voice identification signals.

Referring to FIG. 3 which is a block diagram of a known and most basic conventional first pilot signal detection circuit, the pilot signal detection circuit receives a second audio signal A and extracts a pilot signal P. Center frequency to
A band-pass filter (BPF) 1 of 5f _H , an AM detector 21 that AM-detects the pilot signal P and extracts the modulation signal M, and a center frequency 117.5 Hz for the stereo identification signal S that passes the modulation signal M, respectively. BPF22
And center frequency 274.1H for dual voice identification signal D
The BPF 23 of z and the amplitude evaluation circuit 2 for evaluating the amplitude of the signals S and D supplied and determining the broadcast mode being received.
4 and.

The operation will be described. The second audio signal A
Is supplied to the BPF1, which is the second audio signal A
Signal near 3.5 f _H is passed and only pilot signal P is extracted. This pilot signal P is an AM detector 21.
And is supplied to the BPFs 22 and 23 as a modulated signal M. When the broadcast being received is a stereo broadcast, the modulation signal M is 117.5 Hz, so that it passes through the BPF 22 and the corresponding stereo identification signal S is output. In the case of dual audio broadcasting, the modulation signal M is 274.1 Hz.
Therefore, the signal passes through the BPF 23 and the corresponding double voice identification signal D is output. The amplitude evaluation circuit 24 uses the signals S,
The amplitude of D is evaluated, the identification signal with the larger amplitude is used to determine the broadcast mode being received, and the mode of the audio signal to be output is appropriately switched according to the determination result.

This first conventional pilot signal detection circuit has a detection sensitivity of stereo and dual voice identification signals S and D of A.
It largely depends on the selection characteristics of the BPFs 22 and 23 after M detection. In order to improve the selection characteristics, it is necessary to secure a high Q of these BPFs, but this becomes a difficult factor in reducing the allowable deviation of the center frequency in manufacturing and making it into an IC.

Japanese Patent Laid-Open No. 2-1057 which solves this problem
Referring to FIG. 4 which is a block diagram showing a conventional second pilot signal detection circuit described in Japanese Patent Publication No. 84, a BPF 1 for extracting a pilot signal P common to the first conventional example, a pilot signal P and a reference signal g _{1 ( t)} , g _{2 (t)} , g _{3 (t)} , and g
_{4 (t)} is multiplied with each of the signals P ₁ , P ₂ , P
Multipliers 6, 7, 8, and 9 for generating ₃ and P _4.
And an adder 10 for adding the signals P ₁ and P ₂ to generate a signal U ₁ , an adder 11 for adding the signals P ₃ and P ₄ to generate a signal U ₂ , and signals U ₁ and U ₂ respectively. low-pass filter for generating a respective signal V _1, V ₂ to remove the harmonics (L
PF) 12, 13 and an amplitude evaluation circuit 14 for judging the broadcast mode being received by evaluating the amplitude of the signals V ₁ , V ₂ supplied, and the reference signals g _{1 (t)} , g _{2 (t)} , and a reference signal generation circuit 16 for generating g _{3 (t)} and g _{4 (t)} .

The operation will be described. The pilot signal P extracted by the BPF 1 is supplied to one input terminal of each of the multipliers 6-9. The reference signals g _{1 (t) to} g _{4 (t)} are supplied to the other input terminals of the multipliers 6 to 9, respectively. The multipliers 6 to 9 are generally mixers, and are configured by using non-linear elements such as diodes or parallel modulators. The reference signals g _{1 (t) to} g _{4 (t)} are pilot signals P
Signal with the same frequency of 3.5 f _H as the carrier wave of f and the same f _{H as} the identification signals for stereo and dual audio
It is a composite signal with a signal having a frequency of / 18, f _H / 57. Here, since the difference between the stereo and dual audio identification signals is only in frequency, hereinafter, for convenience of description, only the stereo identification signal will be described.

The signals g _{1 (t) to} g _{4 (t)} are expressed by the following mathematical expressions.

[0010] _{g 1 (t) = cosω p} t · cosω s t g 2 (t) = sinω p t · sinω s t g 3 (t) = sinω p t · cosω s t g 4 (t) = cosω p _{t · sinω s t ω p t} : the pilot signal carrier frequency (3.5f _H) ω _s t: stereo identifying signal modulation frequency (f _H / 18 = 1
77.5 Hz) In addition, pilot signal P supplied via BPF1
Since = f (t) is AM-modulated, it is expressed by the following equation.

F (t) = A {1 + k · cos (ω _s t +
_{φ)} · cos (ω s} t + θ) Here, phi, theta modulated stereo identifying signal is respectively received signals and the pilot signal carrier and the reference signal g
The phase difference between _{1 (t) and} g4 _(t) is shown.

The pilot signal f (t) is respectively multiplied by the reference signals g _{1 (t) to} g _{4 (t)} in each of the multipliers 6 to 9, and the multiplication result signals P1 and P2 of each of the multipliers 6 and 7 are obtained. To the adder 10 and the multiplication result signals P3 and P3 of the multipliers 8 and 9, respectively.
P4 is supplied to each adder 11. Adder 10,
Each of 11 is a signal P1, P2 and a signal P3, respectively.
The addition of P4 is executed and the addition result signals U1 and U2 are supplied to the LPFs 12 and 13, respectively. The LPFs 12 and 13 remove harmonic components of the signals U1 and U2, respectively, to generate signals V1 and V2, and supply these signals V1 and V2 to the amplitude evaluation circuit 14. The amplitude evaluation circuit 14 evaluates the amplitudes of the signals V1 and V2 to determine the multiplex audio mode during broadcasting.

The above processing is shown by the following mathematical expressions.

First, the calculation in the multiplier 6 is expressed by the equation (1). _{f (t) · g 1 (} t) = A {1 + k · cos (ω s t + φ)} · cos (ω s t + θ) · cosω p t · cosω s t = A (1/4) {cos (2ω p t + ω _s t + θ) + cos (2ω _p t−ω _s t + θ) + cos (ω _s t + θ) + cos (ω _s t−θ) + (k / 2) cos (2ω _p t + 2ω _s t + θ + φ) + (k / 2) cos ( _{2ω p t-2ω s t +} θ + φ) + (k / 2) cos (2ω p t + θ + φ) + (k / 2) cos (2ω p t + θ- φ) + (k / 2) cos (2ω s t + θ + φ) + (k / _{2) cos (2ω s t +} φ- θ) + (k / 2) cos (θ + φ) + (k / 2) cos (φ-θ) ............... (1) Similarly, operation in the multiplier 7-9 Are (2)-
It is shown by the equation (4).

[0015] _{f (t) · g 2 (} t) = A (1/4) {- cos (2ω p t-ω s t + θ) + cos (2ω p t + ω s t + θ) + cos (ω s t-θ) -cos _{(ω s t + θ) +} (k / 2) cos (2ω p t + 2ω s t + θ + φ) - (k / 2) cos (2ω p t-2ω s t + θ-φ) + (k / 2) cos (2ω p t + θ-φ ) - (k / 2) cos (2ω p t + θ + φ) + (k / 2) cos (2ω s t + θ-φ) - (k / 2) cos (2ω s t + φ + θ) + (k / 2) cos (θ + φ )-(K / 2) cos (φ−θ) ………… (2) f (t) · g _{3 (t)} = A (1/4) {sin (2ω _p t + ω _s t + θ) + sin (2ω _{p t-ω s t + θ} ) -sin (ω s t + θ) -sin (ω s t-θ) + (k / 2) sin (2ω p t + 2ω s t + θ + φ) + (k / 2) sin (2ω p t- 2 ω _s t + θ-φ) + ( k / 2) sin (2ω p t + θ + φ) + (k / 2) sin (2ω p t + θ- φ) + (k / 2) sin (2ω s t + θ + φ) - (k / 2) sin ( θ−2ω _s t−φ) + (k / 2) sin (θ + φ) − (k / 2) sin (θ−φ) ………… (3) f (t) · g _{4 (t)} = A _{(1/4) {sin (2ω p} t + ω s t + θ) -sin (2ω p t-ω s t + θ) + sin (ω s t + θ) + sin (ω s t-θ) + (k / 2) sin (2ω p t + 2ω _s t + θ + φ)-(k / 2) sin (2ω _p t-2ω _s t + θ-φ)-(k / 2) sin (2ω _p t + θ + φ) + (k / 2) sin (2ω _p t + θ-φ) + ( _{k / 2) sin (2ω s} t + θ + φ) + (k / 2) sin (2ω s t + φ- θ) + (k / 2) sin (θ + φ) + (k / 2) sin (θ-φ) ............ … (4 ) Output signals V1 = v ₁ (t) of the LPFs 12 and 13,
V2 = v ₂ (t) is expressed by equations (5) and (6), respectively. _{v 1 (t) = {f} (t) · g 1 (t) + f (t) · g 2 (t)} T (s) = A (1/4) [(k / 2) {cos (θ + φ) + Cos (φ−θ)} + (k / 2) {cos (θ + φ) −cos (φ−θ)} = (k / 4) Acos (φ + θ) ………………………………………… _{............ (5) v 2 (t} ) = {f (t) · g 3 (t) + f (t) · g 4 (t)} T (s) = A (1/4) [(k / 2) {-sin (θ + φ) -sin (θ-φ)}-(k / 2) {sin (θ + φ) -sin (θ-φ)} =-(k / 4) Asin (φ + θ) ... ………………………………… (6) where T (s) is the transfer function of the LPFs 12 and 13.

The amplitude evaluation circuit 14 is provided with these signals V1 and V1.
The amplitude term A of the identification signal is detected from 2. There are several possible detection methods, but as shown in equation (7), 2
1 of each of the two signals V1 and V2 after squared and added
It is done by squaring. {V ₁ (t) ² + v ₂ (t) ² } ^1/2 = (k / 4) A ………………………… (7) Sufficient cutoff frequency of LPFs 12 and 13 for harmonic removal By setting it low, the detection characteristics of the identification signal can be improved equivalently. For example, the cutoff frequency is 1
If it is lowered to about Hz, the frequency of the stereo identification signal becomes 11
It can detect 7.5 Hz with an accuracy of ± about 1 Hz.

[0017]

The conventional first pilot signal detection circuit described above has an AM detection sensitivity of the identification signal.
After detection, each B for stereo, dual voice identification signal selection
Since it largely depends on the selection characteristics of the PF, it is necessary to secure a high Q of these BPFs in order to improve the selection characteristics, and it is difficult to reduce the yield and to make ICs due to the small allowable deviation of the frequency characteristics in manufacturing. There is a drawback.

A second conventional pilot signal detection circuit that overcomes the above drawback is an LP for removing a harmonic component after calculation.
It is necessary to set the cutoff frequency of F to a small value of about several Hz in order to improve the detection accuracy, and there is a disadvantage that the detection characteristic takes a long time because the response characteristic of the transmission signal becomes slow.

Further, since the pilot signal is directly supplied to the multiplier, it is necessary to sufficiently increase the linearity and the dynamic range of the multiplier in order to secure the detection accuracy in consideration of noise mixing in the weak electric field. There is a drawback that it increases the manufacturing cost.

[0020]

A pilot signal detection circuit of the present invention amplitude-modulates a carrier signal of a predetermined third frequency with first and second identification signals of a first and a second frequency, respectively. In a pilot signal detecting circuit which receives the supply of the generated pilot signal and detects which of the first and second frequencies it is, thereby identifying which of the first and second identification signals it is. A first reference signal that is a first circular function of the third frequency and a second reference signal that is a second circular function of the third frequency, respectively, First and second multiplication circuits for respectively generating first and second multiplication signals, and first and second filter signals for performing predetermined low-pass filtering in response to the supply of the first and second multiplication signals. Respectively output First and second low-pass filter circuits, and the first filter signal and a third reference signal that is a first circular function of the first frequency to multiply to generate a third multiplication signal. A third multiplication circuit for multiplying the second filter signal by a fourth reference signal that is a second circular function of the first frequency to generate a fourth multiplication signal. A circuit, a fifth multiplication circuit that multiplies the first filter signal and the fourth reference signal to generate a fifth multiplication signal, the second filter signal, and the third reference signal A sixth multiplication circuit for generating a sixth multiplication signal by multiplying by, a first addition circuit for adding the third and fourth multiplication signals to generate a first addition signal, and a fifth addition circuit Sixth
Second adder circuit for adding the multiplied signals of 1 to 2 to generate a second added signal, and third and fourth filters for performing predetermined low-pass filtering in response to the supply of the first and second added signals. Third and fourth low-pass filter circuits for respectively outputting signals, and an amplitude evaluation circuit for performing amplitude evaluation in response to the supply of the third and fourth filter signals to detect the first identification signal, And a reference signal generating circuit for generating the first to fourth reference signals.

The pilot signal detection circuit of the present invention includes a pilot signal generated by amplitude-modulating a carrier signal having a predetermined third frequency with first and second identification signals having first and second frequencies, respectively. In the pilot signal detecting method, which receives the supply and identifies which of the first and second identification signals is detected by detecting which of the first and second frequencies, the pilot signal and the pilot signal A first reference signal that is a first circular function of a third frequency and a second reference signal that is a second circular function of the third frequency are respectively multiplied to obtain first and second multiplication signals. In response to the supply of the first and second multiplication signals, predetermined low-pass filtering is performed, and first and second filter signals are respectively output, and the first filter signal and the first filter signal are output. Frequency By multiplying the third reference signal is the first circle function to generate a third multiplied signal, a fourth is a second circular function of the second filter signal and the first frequency
Is multiplied by the reference signal to generate a fourth multiplication signal, the first filter signal is multiplied by the fourth reference signal to generate a fifth multiplication signal, and the second filter signal is generated. Is multiplied by the third reference signal to generate a sixth multiplication signal, the third and fourth multiplication signals are added to generate a first addition signal, and the fifth and sixth multiplication signals are generated. The signals are added to generate a second added signal, predetermined low-pass filtering is performed in response to the supply of the first and second added signals, and third and fourth filtered signals are output, respectively. Amplitude evaluation is performed in response to the supply of the third and fourth filter signals to detect the first identification signal.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Next, referring to FIG. 1, which is a block diagram in which components common to those of FIG. 4 are designated by common letters / numerals, the embodiment of the present invention shown in FIG. The pilot signal detection circuit has the same BPF1 as the second conventional technique.
, Multipliers 6 to 9, adders 10 and 11, and LPF1
2 and 13 and the amplitude evaluation circuit 14, multiplication for multiplying each of the pilot signal P and each of the reference signals e _{1 (t)} and e _{2 (t)} to generate signals R ₁ and R ₂ , respectively. Units 2 and 3 and a low-pass filter (LP which removes harmonic components of signals R ₁ and R ₂ and outputs signals Q 1 and Q 2 respectively)
F) Adder 10 for adding 4 and 5 to generate the signal U _1.
And a reference signal e instead of the conventional reference signal generation circuit 16.
A reference signal generation circuit 15 for generating _{1 (t)} , e _{2 (t)} , h _{1 (t)} and h _{2 (t)} is provided.

Next, the operation of this embodiment will be described with reference to FIG. 1. The pilot signal P extracted by the BPF 1 is supplied to one input terminal of each of the multipliers 2 and 3. The reference signals e _{1 (t)} and e _{2 (t)} are supplied to the other input terminals of the multipliers 2 and 3, respectively. Reference signal e
_{1 (t)} and e _{2 (t)} are signals having the same frequency of 3.5 f _H as the carrier wave of the pilot signal P, and are represented by the following equations.

[0024] _{e 1 (t) = cosω p} t e 2 (t) = sinω p t The pilot signals P supplied via the BPF1
= F (t) is expressed by the following equation as described in the related art.

F (t) = A {1 + k.cos (ω _s t +
_{φ)} · cos (ω s} t + θ) Here, phi, theta modulated stereo identifying signal is respectively received signals and the pilot signal carrier and the reference signal e
The phase difference between _{1 (t)} and e _{2 (t)} is shown.

The pilot signal f (t) is multiplied by the reference signals e _{1 (t)} and e _2t) in the multipliers ₂ and 3, respectively, and the multiplication result signals R1 and R of the multipliers 2 and 3 are multiplied.
2 is supplied to LPFs 4 and 5, respectively, and signals Q1 and Q2 from which harmonic components have been removed are generated.

The output signals R1 and R2 of the multipliers 2 and 3 are expressed by equations (8) and (9), respectively. R1 = f (t) · e _{1 (t)} = A {1 + cos (ω _s t + φ)} cos (ω _p t + θ) cos ω _p t = (A / 2) cos (2ω _p t + θ) + (A / 4) k _{{cos (2ω p t + ω} s t + θ + φ) + cos (2ω p t-ω s t + θ-φ)} + (A / 2) cosθ + (A / 4) k {cos (ω s t + θ + φ) + cos (2 ω s t + φ-θ ) …………………………………………………………………… (7) R2 = f (t) ・ e _{2 (t)} = A {1 + cos (ω _s t + φ) _{} cos (ω p t + θ} ) sinω p t = (A / 2) sin (2ω p t + θ) + (A / 4) k {sin (2ω p t + ω s t + θ + φ) + sin (2ω p t-ω s t + θ-φ) } - (A / 2) sinθ- (A / 4) k {sin (ω s t + θ + φ) -sin (2 ω s t + φ-θ) ...................................................... ……… ......... (8) These signals R1, R2 each output signal Q1 of the corresponding LPF4,5 after passing, Q2, respectively (9), (10)
It is shown by the formula. _{Q1 = f (t) · e} 1 (t) · T 1 (s) = (A / 2) cosθ + (A / 4) k {cos (ω s t + θ + φ) + cos (ω s t + φ-θ) ............ ………………………………………………………… (9) Q2 = f (t) ・ e _{2 (t)}・ T ₂ (s) ＝-(A / 2) sinθ- (A / 4) k { sin (ω s t + θ + φ) -sin (ω s t + φ-θ) ........................................................................ (10 ) Where T ₁ (s) and T ₂ (s) are LPFs 4, 5 respectively.
Is the transfer function of.

The signal Q1 is supplied to one input end of the multipliers 6 and 8, and the signal Q2 is supplied to one input end of one of the multipliers 7 and 9, respectively. On the other hand, the reference signal h _{1 (t)} is supplied to the other input ends of the multipliers 6 and 9, and the reference signal h _{2 (t)} is supplied to the other input ends of the multipliers 7 and 8. These h _{1 (t)} and h _{2 (t)}
Are the same signals as the signals of the frequencies f _H / 18 and f _H / 57 which are the same as the respective identification signals for stereo and dual audio, respectively, and are shown by the following equations (11) and (12).
Here, since the difference between the stereo and dual voice identification signals is only in frequency, hereinafter, only the stereo identification signal will be described for the sake of convenience of description, like the second conventional circuit.

H _{1 (t)} = cos ω _s t …………………………………………………… (11) h _{2 (t)} = sin ω _s t ……………… (12) The output signals P1 and P2 of the multipliers 6 and 7 are added to the adder 10 respectively.
In addition, the output signals P3 and P4 of the multipliers 8 and 9 are supplied to the adder 11, respectively, and are generated as addition signals U1 and U2, respectively. Each of the LPFs 12 and 13 receives the added signals U1 and U2, removes the harmonic components to generate signals V1 and V2, and supplies these signals V1 and V2 to the amplitude evaluation circuit 14. The amplitude evaluation circuit 14 evaluates the amplitudes of the signals V1 and V2 to determine the multiplex audio mode during broadcasting.

The operations of the multipliers 6 to 9 are (13) to
It is shown by the equation (16).

P1 = f (t) · e _{1 (t)} · T ₁ (s) · h _{1 (t)} = (A / 2) cos θ + (A / 4) k {cos (ω _s t + θ + φ) + cos (ω _s t + φ−θ) cos ω _s t = (A / 2) cos θ cos ω _s t + (A / 8) k {cos (2ω _s t + φ + θ) + cos (φ + θ)} + (A / 8) k {cos (2ω _s t + φ− θ) + cos (φ−θ)} (13) P2 = f (t) · e _{2 (t)} · T ₂ (s) · h _{2 (t)} = [− (A / 2) sin θ + (A / 4 _{) k {sin (ω s t} + θ + φ) -sin (ω s t + φ-θ) sinω s t = - (A / 2) sinθcosω s t + (A / 8) k {cos (2ω s t + φ + θ) -cos (φ + θ) } + (A / 8) k {cos (2ω s t + φ-θ) -cos (φ-θ)} ... (14) P3 = f (t) · e 1 (t) · T 1 (s) · h 2 _{(t) = (A / 2} ) co θ + (A / 4) k {cos (ω s t + θ + φ) + cos (ω s t + φ-θ) sinω s t = (A / 2) cosθsinω s t + (A / 8) k {sin (2ω s t + φ + θ) -sin (φ + θ)} + ( A / 8) k {sin (2ω s t + φ + θ) -sin (φ-θ)} ... (15) P4 = f (t) · e 2 (t) · T 2 (s) · h _{1 (t) = [- (} A / 2) sinθ + (A / 4) k {sin (ω s t + θ + φ) -sin (ω s t + φ-θ) cosω s t = - (A / 2) sinθcosω s t - ( a / 8) k {sin ( 2ω s t + φ + θ) + sin (φ + θ)} + (a / 8) k {sin (2ω s t + φ + θ) + sin (φ-θ)} ... (16) multiplied signal of the multiplier 6-9 P1~P4 output signal of each of LPF12,13 having passed through the added low-pass filter as described above V1 = v ₁ (t) V2 = v ₂ (t), respectively (17), represented by equation (18).

V1 = v ₁ (t) = {f (t) e _{1 (t)} T ₁ (s) h _{1 (t)} + f (t) e _{2 (t)} T ₂ (s) h _{2 (t)} } T ₃ (s) = (k / 4) Acos (φ-θ) ……………………………………………… (17) V2 = v ₂ (t) = {f (t _{) e 1 (t) T 1} (s) h 2 (t) + f (t) e 2 (t) T 2 (s) h 1 (t)} T 4 (s) = - (k / 4) Asin ( φ-θ) ………………………………………… (18) where T ₃ (s) and T ₄ (s) are LPF1 respectively.
2 and 13 transfer functions.

The expressions (17) and (18) are the same as the conventional expressions (5) and (6) except that the phase terms are different. Therefore, these signals V1 and V2 are equivalent to the conventional signals V1 and V2. Signal.

The amplitude evaluation circuit 14 receives these signals V1, V
The amplitude term A of the identification signal is detected from 2. As before,
1 after squaring each of the two signals V1 and V2 and adding
/ It is done by raising the power of 2. {V ₁ (t) ² + v ₂ (t) ² } ^1/2 = (k / 4) A …………………… (19) Equation (19) also represents the conventional detection output (7). Identical to the equation, and thus the circuit of this embodiment gives the same result as the conventional second circuit.

In the circuit of this embodiment, the multipliers 2 and 3 for preprocessing and the LPFs 4 and 5 are preliminarily provided on the input side, whereby B
PF1 and multipliers 6 to 9 and LPFs 12 and 1 for this processing
The burden of 3 can be reduced. That is, by setting the cutoff frequency of the LPFs 4 and 5 to about 300 Hz,
The equivalent Q of F1 can be improved to about 91, noise can be effectively removed, and the cutoff frequency of the LPFs 12 and 13 can be set higher than in the prior art, so that the time required for detection can be reduced. In addition, the requirement for linearity for the multiplier and the filter element can be relaxed.

[0036]

As described above, according to the pilot signal detecting circuit and the pilot signal detecting method of the present invention, the pilot signal is extracted by providing the input side with the preprocessing multiplication circuit and the low-pass filter circuit. Since the equivalent Q of the BPF for use in processing is improved and the requirement of linearity for the multiplier and filter element for this processing can be relaxed, it is possible to eliminate the manufacturing difficulty factor.

Since noise can be effectively removed, the cutoff frequency of the LPF can be set high, and the time required for detection can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a pilot signal detection circuit of the present invention.

FIG. 2 is an explanatory diagram showing a frequency spectrum of a two-carrier voice multiplexed signal.

FIG. 3 is a block diagram showing a conventional first pilot signal detection circuit.

FIG. 4 is a block diagram showing a second conventional pilot signal detection circuit.

[Explanation of symbols]

 1,2,23 BPF 2,3,6-9 Multiplier 4,5,12,13 LPF 10,11 Adder 14,24 Amplitude evaluation circuit 15,16 Reference signal generation circuit 21 AM detector

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H04S 1/00 N

Claims (3)

[Claims] 1. A pilot signal generated by amplitude-modulating a carrier signal of a predetermined third frequency with first and second identification signals of first and second frequencies, respectively, and receiving the first signal. , A pilot signal detecting circuit for identifying which of the first and second identification signals is detected by detecting which of the second frequencies, the first of the pilot signal and the third frequency And a second reference signal, which is a second circular function of the third frequency, respectively, to generate first and second multiplied signals, respectively. A second multiplication circuit, and first and second low-pass filters that perform predetermined low-pass filtering in response to the supply of the first and second multiplication signals and output first and second filter signals, respectively. A circuit, and the first A third multiplying circuit for generating a third multiplied signal by multiplying the second filtered signal with the third reference signal that is the first circular function of the first frequency; the second filtered signal; A fourth multiplication circuit for generating a fourth multiplication signal by multiplying with a fourth reference signal which is a second circular function of a first frequency; the first filter signal and the fourth reference signal A fifth multiplication circuit for generating a fifth multiplication signal by multiplying by and a sixth multiplication circuit for multiplying the second filter signal by the third reference signal to generate a sixth multiplication signal A circuit, a first addition circuit that adds the third and fourth multiplication signals to generate a first addition signal, and a circuit that adds the fifth and sixth multiplication signals to generate a second addition signal A second adder circuit, which performs predetermined low-pass filtering in response to the supply of the first and second adder signals; Third and fourth low-pass filter circuits for respectively outputting the first and fourth filter signals, and amplitude evaluation is performed in response to the supply of the third and fourth filter signals to detect the first identification signal. A pilot signal detection circuit comprising an amplitude evaluation circuit and a reference signal generation circuit for generating the first to fourth reference signals. 2. The amplitude evaluation circuit comprises the third and fourth circuits.
2. The pilot signal detection circuit according to claim 1, wherein the amplitude evaluation is performed by squaring each of the filter signals of 1 above, adding the squared sums, and then squaring the sum. 3. A pilot signal generated by amplitude-modulating a carrier signal having a predetermined third frequency with first and second identification signals having first and second frequencies, respectively, and receiving the first signal. , A pilot signal detecting method for identifying which one of the first and second identification signals is detected by detecting which one of the second frequencies, the first of the pilot signal and the third frequency The first reference signal, which is a circular function of, and the second reference signal, which is a second circular function of the third frequency, are respectively multiplied to generate first and second multiplied signals, respectively. In response to the supply of the first and second multiplication signals, predetermined low-pass filtering is performed to output first and second filter signals, respectively, and the first circle of the first filter signal and the first frequency Third reference signal that is a function And a fourth reference signal, which is a second circular function of the first frequency, to generate a third multiplied signal, and a fourth multiplied signal is generated. To generate a fifth multiplied signal by multiplying the first filter signal by the fourth reference signal, and multiplying the second filter signal by the third reference signal by 6 to generate a multiplication signal, add the third and fourth multiplication signals to generate a first addition signal, add the fifth and sixth multiplication signals to generate a second addition signal, In response to the supply of the first and second addition signals, predetermined low-pass filtering is performed to output third and fourth filter signals, respectively, and in response to the supply of the third and fourth filter signals. A pilot signal detection method, characterized in that amplitude evaluation is performed to detect the first identification signal. .